Western Bean Cutworm Moth Look-a-like

July 31, 2023

One of the most common pests we monitor for in our Ohio Lepidopteran Monitoring Network is the Western bean cutworm (WBC). The WBC caught the attention of growers across the state around 2017, when it became apparent that the caterpillars were developing resistance to the Bt trait in corn that had previously provided protection. With WBC numbers increasing across the state, we expanded our monitoring network to include more counti es to try to understand the population in Ohio. 

To monitor, Extension educators and volunteers across the state set bucket traps with a lure to attract adult male moths. Traps are set from mid-June until mid-August and checked weekly for moths. Data is then entered into an online spread sheet where averages are calculated weekly and reported in the C.O.R.N. newsletter. We recommend scouting for WBC egg masses in corn when county averages are 7 or more moths per week. 

In order to ensure our trap counts are accurate, we provide images of the moths to assist with identification. In addition, the lures used to attract the moths is specific to the pest - but there have been instances where similar species find their way into traps.

Two basic identification characteristics for the WBC that we try to look for are the boomerang structure on the wings and the dot located right above the boomerang. In addition, WBC moths fold their wings flat. Despite these key characteristics, identification can be difficult because the wings deteriorate in the trap. 

Recently we have noticed a WBC look-a-like in the blacklight traps we monitor in Wooster, OH. This moth has a similar boomerang marking on its wings, with the dot just above the marking. Additionally, the wings lay flat, similar to WBC. So what is this look-a-like? After some digging around, we deteremined it to be the flame-shouldered dart moth. This species could easily be mistaken for WBC - however, it does have one key characteristic to distinguish it from WBC, and that is its size. The flame-shouldered dart moth is noticably smaller than WBC measuring around 15 mm whereas WBC is approximately 20 mm. 

The good news is the flame-shouldered dart is not a pest of agronomic crops. But the big question is are they attracted to the WBC lure? That has yet to be determined, but we do want to draw attention to the look-a-like so that when our network is monitoring we are paying attention to moth size when counting WBC numbers.